5 Common channel management procedures

08.583GPPBase Station Controler - Base Transceiver Station (BCS-BTS) Interface Layer 3 SpecificationRelease 1999TS

5.1 Channel request by MS

The procedure is initiated by TRX upon detection of a random access from an MS (CHANnel REQuest message from MS). TRX then sends a CHANnel ReQuireD message to BSC containing the Request Reference parameter (random number selected by MS plus some low order bits of the TDMA frame number for the access) and the measured delay of the Access Burst.

5.2 Paging

This procedure is used to request the paging of one mobile station on a given paging subchannel.

The paging of an MS is initiated by BSC sending a PAGing CoMmanD message to BTS. The message contains the MS identity (TMSI or IMSI), the paging population number of the MS, optionally an indication for the MS about which combination of channels will be needed for the subsequent transaction related to the paging and optionally an indication of the eMLPP priority of the call.

The PAGing REQuest messages to be sent on the radio path are built and sent by BTS.

The use by BTS of the "extended paging" facilities and the general downlink scheduling of the downlink CCCH is operator dependant and is not specified in this GTS. This process may also be influenced by O&M procedures.

5.3 Delete indication

This procedure is used by BTS to indicate that due to overload on the downlink CCCH, an IMMEDIATE ASSIGN COMMAND has been deleted.

For that purpose BTS sends a DELETE INDication message to BSC.

5.4 CCCH load indication

This procedure is used by a BTS to inform the BSC of the load on a particular CCCH timeslot.

The CCCH LOAD INDication message is sent regularly from BTS to BSC if the load exceeds some value set by O&M. The sending rate is also set by O&M.

5.5 Broadcast information modify

This procedure is used by BSC to indicate to BTS the new information to be broadcast on BCCH.

For that purpose, BSC sends a BCCH INFOrmation message to BTS.

5.6 Short Message Cell Broadcast

Short Message Service Cell Broadcast messages are sent to BTS as SMS BROADCAST REQUEST or SMS BROADCAST COMMAND messages.

With the SMS BROADCAST REQUEST mode of operation, the BSC handles the queuing, repetition and transmission of the messages taking the capacity of the CBCHs (basic and extended channel (see 3GPP TS 05.02)) into account. The BSC is also responsible for the segmentation of the SMS Cell Broadcast messages on the Radio interface:

With the SMS BROADCAST COMMAND mode of operation, the BSC can request the broadcast of a complete Cell Broadcast message. The BSC handles the queuing, repetition and transmission of the messages taking the capacity of the CBCHs (basic and extended channel [see 3GPP TS 05.02]) into account. The BSC is responsible for the segmentation of the SMS Cell Broadcast messages on the Radio interface:

With the SMS BROADCAST COMMAND mode of operation, the BSC can also set the BTS broadcast default mode. The BTS is then responsible for transmission of a default message when no other message is to be broadcast.

Even though BSC handles the transmission of messages taking the capacity of CBCH into account, BTS can indicate to BSC if an overflow or underflow situation is about to happen in the CBCH. With the CBCH LOAD INDICATION mode of operation, the BTS can request immediate broadcast of m (=amount indicated in the CBCH Load Information element) scheduled SMSCB messages in the underflow situation. BSC shall transmit m scheduled messages and after that continue the broadcast of messages according to its own timetable. If BTS requests more messages than BSC is possessing, then BSC shall transmit only the amount it is possessing. CBCH LOAD INDICATION mode of operation could only be applied when DRX mode is used (see 3GPP TS 04.12).

With the CBCH LOAD INDICATION mode of operation, the BTS can also request immediate stop of broadcast for a period of m (=amount indicated in the CBCH Load Information element) message slots in the overflow situation. BSC shall stop the broadcast for a period of m message slots and after that continue the broadcast of messages according to its own timetable.

5.7 IMMEDIATE ASSIGNMENT

This procedure is used by BSC to request the transmission of an immediate assign message on downlink CCCH. To initiate the immediate assign, the BSC sends an IMMEDIATE ASSIGN COMMAND message. The message contains the complete immediate assign message as defined in 3GPP TS 04.08 (IMMEDIATE ASSIGNMENT or IMMEDIATE ASSIGNMENT EXTENDED or IMMEDIATE ASSIGNMENT REJECT) with the "Page Mode" element set to the value "no change". Upon receipt of the message, the BTS may transmit the immediate assignment message as received or combine several to construct the IMMEDIATE ASSIGNMENT EXTENDED or IMMEDIATE ASSIGNMENT REJECT. The BTS may also update the "Page Mode" element before transmission.

The IMMEDIATE ASSIGNMENT EXTENDED message is either sent by the BSC in the IMMEDIATE ASSIGN COMMAND, or built by the BTS from up to two IMMEDIATE ASSIGN COMMAND messages.

The IMMEDIATE ASSIGNMENT REJECT message is either sent by the BTS as received in the IMMEDIATE ASSIGN COMMAND message or built by the BTS from the contents of two or more IMMEDIATE ASSIGN COMMAND messages. For the latter case the BTS may consider request references with identical contents within the same message as duplicates and all but one may be suppressed.

5.8 Notification

This procedure is used to request that notification be performed by the BTS. The BSC indicates the exact action required by the BTS in the command indicator.

The NOTIFication messages to be sent on the radio path are built and sent by BTS.

The BSC manages the NCH DRX information whilst the BTS manages the scheduling of the messages on the NCH.

If the BTS for some reason can not perform the notification commanded by the BSC, then the BTS shall return an ERROR REPORT message with the relevant cause value.